This invention relates to aspiration and evacuation systems for surgical instruments, such as intraocular vitrectomy units. The invention is particularly useful as an aspirating and evacuating system for the pneumatic intraocular surgical handpiece disclosed in copending U.S. patent application Ser. No. 097,984, filed on even date herewith, invented by Maxwell D. Helfgott, M.D. and Gerald N. Helfgott, and entitled "Powered Handpiece For Endophthalmic Surgery".
Before one may appreciate all the features of the aspirating and evacuating system described herein, one must first have some understanding of the surgical instruments such systems are commonly applied to. One such surgical instrument is the intraocular vitrectomy unit used for removing vitreous tissue within the eyes of humans or animals.
Intraocular vitrectomy units are basically comprised of a handpiece including a short, elongated cutting tube mounted onto a handle. The cutting tube is operated by a pneumatic or electric power source connected to the handle of the unit. In some ways, the cutting tube is structurally similar to a needle valve used to pump air into athletic equipment such as footballs and basketballs. Like a needle valve, the cutting tube is hollow throughout its interior, closed on its distal end, and has a small lateral port near its end for transmitting a pneumatic pressure. However, unlike a needle valve, the cutting tube has either a rotating or reciprocating blade member located within its hollow interior. Further, the lateral port transmits a negative, rather than a positive pneumatic pressure.
During an operation, the cutting tube of the vitrectomy unit is inserted through the wall of the eyeball and into the vitreous tissue and fluids contained therein. An aspirating and evacuating unit is fluidly connected to the hollow interior of the cutting tube, and the lateral port of the tube is manipulated so that a segment of unwanted intraocular tissue is drawn into the port by the negative aspirating pressure, along with some of the vitreous fluids contained within the eyeball. The rotary or reciprocating blade member severs into discrete chunks the tissue drawn into its lateral port by rhythmically shearing it between the edge of the port and the rotating or reciprocating blade. The negative aspirating pressure continues to act on these discrete chunks of tissue and vitreous fluids and withdraws them through the hollow interior of the cutting tube and out of the vitrectomy unit by means of an evacuation conduit.
In addition to aspirating and evacuating systems, intraocular vitrectomy units usually also include irrigation systems which prevent the eyeball from collapsing due to the evacuation of tissue and fluids therefrom. Such irrigation systems positively inject fluid into the interior of the eyeball as the aspirating and evacuating units suck fluids and tissue out of the eye. This way, the net fluid pressure within the eyeball is maintained at the normal level above atmospheric pressure, and all eye components remain in their approximate normal positions during the operation of the vitrectomy unit.
Ideally, an aspirating and evacuating unit for use with a surgical vitrectomy unit should provide a source of aspirating or suction pressure which is easily and accurately controllable in order to minimize the danger of accidentally destroying delicate tissues, such as the retina within the eye. Specifically, the unit should provide a source of suction with "digital" cut off characteristics (i.e., the ability to cut off immediately with respect to time like a square wave function, rather than trailing off gradually with time like an inverse ramp function). Furthermore, the action of the aspirating and evacuating unit should be positively and directly coordinated with the action of the blade of the vitrectomy unit, so that the suction pressure is actuated only during the cutting stroke of the reciprocating blade. Consistent with the preceding requirements, the unit should have suction controls which possess an extremely high degree of mechanical reliability. Such a unit should also be simple in construction in order to facilitate both mass production and reliability. Finally, it would be desirable if such a unit were compatible with a variety of prior art vitrectomy units, rather than just one special type of vitrectomy unit.
Aspirating and evacuating systems for intraocular vitrectomy units are known in the prior art. Examples of such systems are disclosed in U.S. Pat. Nos. 3,812,855, 3,884,237, 3,884,238, 3,920,014, 4,007,742, 4,019,514, and 4,117,843. However, each of the prior art systems disclosed in these patents falls short of fullfilling at least one of the aforementioned ideal criteria.
For example, the suction controller disclosed in U.S. Pat. No. 3,812,855 coordinates the coaction between its pneumatically operated vitrectomy unit and its suction and evacuation system through an electrical interfacing in the form of electrically operated valves. Additionally, the structure of this invention is intricate, utilizing many moving parts. The use of an indirect electrical coordination system in such a complicated device instead of a direct, pneumatic coordination system in a relatively simple device makes simultaneous coaction between the blade and suction unit mechanically more difficult to attain, and increases the chance of equipment malfunction. Finally, this particular invention utilizes flexible tubing between the vitrectomy and the source of suction, and makes no provision for dealing with the residual negative pressure trapped between the suction cut off valves and the vitrectomy unit. Thus a "digital" cut-off of suction pressure is difficult, if not impossible.
The aspiration and evacuation systems disclosed in U.S. Pat. Nos. 3,815,604, 3,884,237 and 3,884,238 also utilize an electrical infacing in the form of a solenoid operated, rotary gate valve for coordinating simultaneous coaction between the suction unit and the vitrectomy unit. Further, no provision is made for eliminating residual negative pressure trapped between the suction tube and the vitrectomy unit. Thus a "digital" cut off of suction pressure is again difficult or impossible. Moreover, the structure of the vacuum control of this invention is complicated by the fact that the suction source functions to reciprocate the blade of the vitrectomy unit as well as to power the aspiration and evacuation system.
Finally, the aspiration and evacuation systems disclosed in U.S. Pat. Nos. 3,920,014, 4,007,772, 4,019,514 and 4,117,843 again utilize an electrical interface to control the coaction of their respective blade units and aspiration and evacuation units. While the aspiration control in each of these inventions recognizes the problems associated with residual negative pressure existing in the suction line between the suction unit and the vitrectomy unit after the suction unit is stopped, the solutions proposed in these patents are very difficult to apply. For example, the 3,920,014 patent suggests reversing the peristaltic suction pump to minimize the residual pressure, or opening the clamping mechanism of the peristaltic pump so that the evacuation line is effectively vented. Either of these solutions would require precisely timed execution in order to effectuate a "digital", essentially instantaneous cut off of the negative aspirating pressure.
The shortcomings of the preceding representative samples of the prior art clearly illustrate the need for an aspiration and evacuation unit capable of directly co-acting with a vitrectomy blade unit without a complicated electropneumatic interface, and further capable of selectively and digitally cutting off the negative pressure of aspiration to avoid damaging delicate tissue.